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1.
Rate constants for the gas-phase reactions of the OH radical with 1-methylnaphthalene and of N2O5 with 1- and 2-methylnaphthalene and 2,3-dimethylnaphthalene have been determined at 298 ± 2 K by use of relative rate techniques. The rate constants determined were: for the reaction of OH radicals with 1-methylnaphthalene, (5.30 ± 0.48) × 10−11 cm3 molecule−1 s−1; for the reaction of N2O5 with 1-methylnaphthalene, 2-methylnaphthalene and 2,3-dimethylnaphthalene, (3.3 ± 0.7) × 10−17, (4.2 ± 0.9) × 10−17 and (5.7 ± 1.9) × 10−17 cm3 molecule−1 s−1, respectively. In addition, an upper limit to the rate constant of 1.3 × 10−19 cm3 molecule−1 s−1 was measured for the reaction of O3 with 1-methylnaphthalene at 298 ± 2 K. These data, when combined with data from previous literature, allow the atmospheric gas-phase removal processes of these alkylnaphthalenes to be quantified.  相似文献   

2.
The rate constants for reactions of the SO4 radical anion with some low molecular weight monocarboxylic acids (MCAs) and dicarboxylic acids (DCAs) and their anions using the laser flash photolysis-long path laser absorption (LFP-LPLA) technique were determined. The present study contains the first measured rate constants for SO4 reactions with glycolic, lactic, malic and malonic acid. The rate constants are found to be in the range from 105 to 107 M−1 s−1, with the lower values found for acids and higher values for their respective anions. In addition, the rate constants for scavenging of SO4 by all investigated organics in the Mn(II)-catalyzed S(IV) autoxidation at pH 4.5 and T=25 °C were determined by means of the reversed rate method. The comparison between these rate constants and the rate constants obtained by direct measurements confirms the proposed inhibiting mechanism for the Mn(II)-catalyzed S(IV) autoxidation in the presence of monocarboxylic acids. In the case of formic acid, which causes the highest inhibition, this mechanism can explain the second part of kinetic traces (i.e. after the induction period). Surprisingly, although dicarboxylic acids are reactive toward SO4 they do not contribute to the inhibition of S(IV) oxidation (especially malic and malonic acids).  相似文献   

3.
The photooxidation of methylhydroperoxide (MHP) and ethylhydroperoxide (EHP) was studied in the aqueous phase under simulated cloud droplet conditions. The kinetics and the reaction products of direct photolysis and OH-oxidation were studied for both compounds. The photolysis frequencies obtained were JMHP=4.5 (±1.0)×10−5 s−1 and JEHP=3.8 (±1.0)×10−5 s−1 for MHP and EHP respectively at 6 °C. The rate constants of OH-oxidation of MHP at 6 °C were 6.3 (±2.6)×108 M−1 s−1 and 5.8 (±1.9)×108 M−1 s−1 relative to ethanol and 2-propanol respectively, and the rate constant of OH-oxidation of EHP was 2.1 (±0.6)×109 M−1 s−1 relative to 2-propanol at 6 °C. The reaction products obtained were not only the corresponding aldehydes, but also the corresponding acids, and hydroxyhydroperoxides as primary reaction products. The yields for these products were sensitive to the pH value. The carbon balance was higher than 85% for all experiments, showing that most reaction products were detected. A chemical mechanism was proposed for each reaction, and the atmospheric implications were discussed.  相似文献   

4.
Rate constants for the atmospheric reactions of 1-methyl-2-pyrrolidinone with OH radicals, NO3 radicals and O3 have been measured at 296±2 K and atmospheric pressure of air, and the products of the OH radical and NO3 radical reactions investigated. Using relative rate techniques, rate constants for the gas-phase reactions of OH and NO3 radicals with 1-methyl-2-pyrrolidinone of (2.15±0.36)×10-11 cm3 molecule-1 s-1 and (1.26±0.40)×10-13 cm3 molecule-1 s-1, respectively, were measured, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference compounds. An upper limit to the rate constant for the O3 reaction of <1×10-19 cm3 molecule-1 s-1 was also determined. These kinetic data lead to a calculated tropospheric lifetime of 1-methyl-2-pyrrolidinone of a few hours, with both the daytime OH radical reaction and the nighttime NO3 radical reaction being important loss processes. Products of the OH radical and NO3 radical reactions were analyzed by gas chromatography with flame ionization detection and combined gas chromatography–mass spectrometry. N-methylsuccinimide and (tentatively) 1-formyl-2-pyrrolidinone were identified as products of both of these reactions. The measured formation yields of N-methylsuccinimide and 1-formyl-2-pyrrolidinone were 44±12% and 41±12%, respectively, from the OH radical reaction and 59±16% and ∼4%, respectively, from the NO3 radical reaction. Reaction mechanisms consistent with formation of these products are presented.  相似文献   

5.
Rate coefficients for the reactions of hydroxyl radicals and chlorine atoms with acrylic acid and acrylonitrile have been determined at 298 K and atmospheric pressure. The decay of the organics was followed using a gas chromatograph with a flame ionization detector (GC-FID) and the rate constants were determined using a relative rate method with different reference compounds. Room temperature rate constants are found to be (in cm3 molecule−1 s−1): k1(OH+CH2CHC(O)OH)=(1.75±0.47)×10−11, k2(Cl+CH2CHC(O)OH)=(3.99±0.84)×10−10, k3(OH+CH2CHCN)=(1.11±0.33)×10−11 and k4(Cl+CH2CHCN)=(1.11±0.23)×10−10 with uncertainties representing ±2σ. This is the first kinetic study for these reactions under atmospheric pressure. The rate coefficients are compared with previous determinations taking into account the effect of pressure on the rate constants. The effect of substituent atoms or groups on the overall rate constants is analyzed in comparison with other unsaturated compounds in the literature. In addition, atmospheric lifetimes based on the homogeneous sinks of acrylic acid and acrylonitrile are estimated and compared with other tropospheric sinks for these compounds.  相似文献   

6.
The night-time tropospheric chemistry of two stress-induced volatile organic compounds (VOCs), (Z)-pent-2-en-1-ol and pent-1-en-3-ol, has been studied at room temperature. Rate coefficients for reactions of the nitrate radical (NO3) with these pentenols were measured using the discharge-flow technique. Because of the relatively low volatility of these compounds, we employed off-axis continuous-wave cavity-enhanced absorption spectroscopy for detection of NO3 in order to be able to work in pseudo first-order conditions with the pentenols in large excess over NO3. The rate coefficients were determined to be (1.53±0.23)×10−13 and (1.39±0.19)×10−14 cm3 molecule−1 s−1 for reactions of NO3 with (Z)-pent-2-en-1-ol and pent-1-en-3-ol. An attempt to study the kinetics of these reactions with a relative-rate technique, using N2O5 as source of NO3 resulted in significantly higher apparent rate coefficients. Performing relative-rate experiments in known excesses of NO2 allowed us to determine the rate coefficients for the N2O5 reactions to be (5.0±2.8)×10−19 cm3 molecule−1 s−1 for (Z)-pent-2-en-1-ol, and (9.1±5.8)×10−19 cm3 molecule−1 s−1 for pent-1-en-3-ol. We show that these relatively slow reactions can indeed interfere with rate determinations in conventional relative-rate experiments.  相似文献   

7.
Conductometry was used to study the kinetics of the oxidation of hydrogen sulfite, HSO3, by hydrogen peroxide in aqueous non-buffered solution at the low concentration level of 10−5–10−6 M, typically found in cloud water. The kinetic data confirm that the rate law reported for the pH range 3–6 at higher concentration levels, rate=kH·[H+]·[HSO3]·[H2O2], is valid at the low concentration level and at low ionic strength Ic. At 298 K and Ic=1.5×10−4 M, third-order rate constant kH was found to be kH=(9.1±0.5)×107 M−2 s−1. The temperature dependence of kH led to an activation energy of Ea=29.7±0.9 kJ mol−1. The effect of the ionic strength (adjusted with NaCl) on rate constant kH was studied in the range Ic=2×10−4–5.0 M at pH=4.5–5.2 by conductometry and stopped-flow spectrophotometry. The dependence of kH on Ic can be described with a semi-empirical relationship, which is useful for the purpose of comparison and extrapolation. The kinetic data obtained are critically compared with those reported earlier.  相似文献   

8.
Aerosol concentrations of methanesulphonic acid (MSA), dimethyl sulphoxide (DMSO) and dimethyl sulphone (DMSO2) have been measured from landbased stations at Plymouth (Devon, U.K.), Galway (EIRE), and from various shipboard stations in the North Sea and the North Atlantic Ocean. MSA, DMSO and DMSO2 all show seasonal cycles with spring/summer maxima and winter minima. The summer concentrations of MSA are approximately an order of magnitude higher than in winter. The general levels of MSA (July 1985 mean = 9.27 × 10−9 mol m−3, December 1986 mean = 1.14 × 10−9 mol m−3) are comparable to those reported from Cape Grim, Tasmania. Modelling indicates that neither MSA nor DMSO2 are present in sufficient quantity to represent major oxidation pathways for dimethyl sulphide (DMS). Rate constant ratios for both the reactions of DMS and DMSO with OH and IO have been estimated. Hydroxyl radical does not appear to be reactive enough for it to be the major sink of atmospheric DMS. It is also shown that the rate constants for the destruction of DMSO (the main reaction product of the DMS/IO system) with either IO or OH are likely to be slow. Thus low tropospheric concentrations of DMSO tend to indicate that it also is not a major product of DMS oxidation.  相似文献   

9.
Using the relative technique, rate coefficients have been measured for the gas phase reactions of hydroxyl radicals with four fluoroacetates, methyl trifluoroacetate (CF3COOCH3), ethyl trifluoroacetate (CF3COOCH2CH3), methyl difluoroacetate (CF2HCOOCH3) and 2,2,2-trifluoroethyl trifluoroacetate (CF3COOCH2CF3). Experiments were carried out at 296±2 K and atmospheric pressure (∼750 Torr) using nitrogen or synthetic air as bath gases. The following rate coefficients were derived for the reaction of OH radicals (in units of cm3 mol−1 s−1) with CF3COOCH3, k=(4.97±1.04)×10−14, CF3COOCH2CH3, k=(2.64±0.59)×10−13, CF2HCOOCH3, k=(1.48±0.34)×10−13 and CF3COOCH2CF3, (1.05±0.23)×10−13. The rate constants obtained are compared with previous literature data of other volatile organic compounds to establish reactivity trends. Atmospheric implications are discussed in terms of lifetimes and fates of the fluoroacetates in the troposphere.  相似文献   

10.
This work deals with the kinetic study of the reactions of ozone with pyrene, 1-hydroxypyrene and 1-nitropyrene, adsorbed on model particles. Experiments were performed at room temperature and atmospheric pressure, using a quasi-static flow reactor in the absence of light. Compounds were extracted from particles using pressurized fluid extraction (PFE) and concentration measurements were performed using gas chromatography/mass spectrometry (GC/MS). The pseudo-first order rate constants were obtained from the fit of the experimental decay of particulate polycyclic compound concentrations versus reaction time. Experiments were performed at three different O3 concentrations from which second order rate constants were calculated. The following rate constant values were obtained at 293 K: k(O3 + Pyrene) = (3.2 ± 0.7) × 10?16 cm3 molecule?1 s?1; k(O3 + 1OHP) = (7.7 ± 1.4) ×10 ?16 cm3 molecule?1 s?1; and k(O3 + 1NP) = (2.2 ± 0.5) × 10?17 cm3 molecule?1 s?1, for pyrene, 1-hydroxypyrene and 1-nitropyrene adsorbed on silica particles. The variation in the rate constants demonstrates the strong influence of the substituent (OH or NO2) on the heterogeneous reactivity of pyrene. The pyrene particulate concentration was also varied in order to check how this parameter may influence the experiments. Finally, oxidation products were investigated for all reactions and some were detected and identified for the first time for ozone heterogeneous reaction with pyrene adsorbed on particles.  相似文献   

11.
Using the relative kinetic technique the kinetics of the gas-phase reactions of Br radicals with acrolein, methacrolein and methylvinyl ketone have been investigated at (301±3) K in 1013 mbar of (N2+O2) bath gas at varying proportions. In 1013 mbar of synthetic air the following rate coefficients have been obtained (in units of cm3 molecule−1 s−1): acrolein (3.21±0.11)×10−12; methacrolein (2.33±0.08)×10−11; methyl vinyl ketone (1.87±0.06)×10−11. This study represents the first determination of the rate coefficients for these compounds. As for other unsaturated hydrocarbons the rate coefficient with Br was found to increase with increasing partial pressure of O2. From the product studies of the reactions it has been established that addition of Br radicals to the terminal C-atom is the major pathway in all three cases. However, for acrolein H atom abstraction from the -CO–H group is also significant. Mechanisms are proposed to explain the observed products, mainly β-brominated carbonyl compounds.  相似文献   

12.
Using the relative rate technique, rate constants for the gas-phase reactions of hydroxyl radicals with 2-chloroethyl methyl ether (k1), 2-chloroethyl ethyl ether (k2) and bis(2-chloroethyl) ether (k3) have been measured. Experiments were carried out at (298 ± 2) K and atmospheric pressure using synthetic air as bath gas. Using n-pentane and n-heptane as reference compounds, the following rate constants were derived: k1 = (5.2 ± 1.2) × 10?12, k2 = (8.3 ± 1.9) × 10?12 and k3 = (7.6 ± 1.9) × 10?12, in units of cm3 molecule?1 s?1. This is the first experimental determination of k2 and k3 under atmospheric pressure. The rate constants obtained are compared with previous literature data and the observed trends in the relative rates of reaction of hydroxyl radicals with the ethers studied are discussed. The atmospheric implications of the results are considered in terms of lifetimes and fates of the hydrochloroethers studied.  相似文献   

13.
The kinetics of the reactions of O3 with 3-bromopropene and 3-iodopropene has been studied over the temperature range of 288–328 K at atmospheric pressure. The results obtained for the room temperature rate constants are (1.88 ± 0.22) × 10?18 and (3.52 ± 0.43) × 10?18 cm3 molecule?1 s?1, and the proposed Arrhenius expressions are k = (3.47 ± 1.28) × 10?15 exp[(?2233 ± 110)/T] and k = (8.17 ± 2.12) × 10?14 exp[(?2991 ± 80)/T] cm3 molecule?1 s?1 for 3-bromopropene and 3-iodopropene, respectively. The atmospheric chemical lifetimes of these two compounds with O3 were also estimated from these values.  相似文献   

14.
采用超声波-电催化联合技术处理2-氯酚(2-CP)和4-氯酚(4-CP),探讨了电催化氧化和超声氧化的协同效应,考察了影响声电联合降解氯酚化合物的条件因数.结果表明,超声波-电催化联合技术处理效率明显优于电催化氧化技术,2-CP和4-CP的增强因子f分别为1.325和1.509.高电流密度有助于氯酚降解,2-CP和4-CP的表观反应速率常数随电流密度上升分别增加了1.28×10-5 s-1和1.82×10-5 s-1;高pH值也有利于氯酚降解,pH为9.08时,2-CP和4-CP的表观反应速率常数分别为9.22×10-5 s-1和11.02×10-5 s-1;高电解质浓度促进了2-CP的降解,而对4-CP的降解影响不大,2-CP表观反应速率常数从7.70×10-5 s-1上升到16.03×10-5 s-1.总之,超声波-电催化联合技术能够协同降解氯酚.  相似文献   

15.
Chemical actinometry was used to measure nitrate photolysis rate coefficients, JNO3, on and in snowpack at Summit, Greenland. Sealed glass tubes containing nitrate and a hydroxyl radical trapping system were buried in snow and exposed for between 2 and 24 h. Average JNO3 values for 2-h midday exposures in early June on surface snow were 10–14×10−7 s−1. Averages over 24 h were 3.5–4.5×10−7 s−1. These values reflect the integrated photon flux and also any variation of the nitrate photolysis rate with temperature. Attenuation of JNO3 within the firn was 0.03–0.04 cm−1 for 24-h exposures and 0.08 cm−1 for a 2-h exposure. Different attenuation coefficients may relate to differential light penetration due to changes in sun angle over the course of 24 h.  相似文献   

16.
《Chemosphere》1987,16(4):681-694
Rate constants for some environmentally important organic model compounds reacting with singlet oxygen in water have been determined in laboratory experiments using rose bengal as a sensitizer. Dimethylfuran, furfuryl alcohol, 2,3-dimethyl-2-butene and diethylsulfide react about three times faster in water than in non-aqueous solutions. Phenolic compounds react faster at higher pH values. Their rate constants exactly increase with their degree of dissociation. Rate constants for the ionized species of these phenolic compounds are greater than 108M−1s−1. In natural surface water under solar irradiation reaction with singlet oxygen is important only for a few classes of especially reactive organic compounds.  相似文献   

17.
A detailed study of resuspension of 1.85 μm MMAD silica particles from five horizontal layers within a small scale spruce canopy was carried out in a wind tunnel in which saplings were exposed to a constant free stream wind speed of 5 m s−1. This provided quantitative estimates of the potential for a tree canopy contaminated with an aerosol deposit to provide (i) an airborne inhalation hazard within the forest environment and (ii) a secondary source of airborne contamination after an initial deposition event. Resuspension occurred with a flux of 1.05×10−7 g m−2 s−1 from spruce saplings initially contaminated at a level of 4.1×10−2 g m−2. An average resuspension rate (Λ) of 4.88×10−7 s−1 was obtained for the canopy as a whole. Values of Λ were significantly different (ANOVA, p<0.001) between canopy layers and Λ was markedly greater at the top of the canopy than lower down although there was a slight increase in Λ at the base of the canopy. The resuspended silica particles deposited onto the soil surface at an average rate of about 5.3×10−8 μg cm−2 s−1. It is concluded that resuspension under wind velocities similar to that used in the reported experiments is likely to pose a relatively small inhalation hazard to humans and a relatively minor source of secondary contamination of adjacent areas. Furthermore, resuspension rates are likely to diminish rapidly with time. The results are discussed in relation to the growing interest in the tree planting schemes in urban areas to reduce the impacts of air pollution.  相似文献   

18.
Dinitrogen pentoxide (N2O5), which is present in equilibrium with NO3 radicals and NO2, has been recognized for some time as an intermediate in the NOx chemistry of night-time atmospheres. However, until the advent of long pathlength spectroscopic techniques for the measurement of atmospheric NO3 radical concentrations, no reliable method for estimating N2O5 concentrations has been available. We have calculated maximum night-time N2O5 concentrations from the available experimentally determined concentrations of the NO3 radical and NO2 in the U.S. and Germany, and find that N2O5 concentrations as high as ~ 15 ppb can occur. We have also estimated removal rates for N2O5 and for NO3 radicals during these nights. From data obtained under conditions devoid of point sources of NOx, upper limit estimates of the homogeneous rate constant for the reaction of N2O5 with water vapor are obtained, leading to the conclusion that the homogeneous gas phase rate constant for this reaction is ⩽ 1 × 10−21 cm3 molecule−1 s−1 at 298 K, consistent with recent environmental chamber data.  相似文献   

19.
A limited survey of rainwater composition covering 80 precipitation events was carried out to establish the levels of soluble metal ions which may influence the oxidation rate of SO2 in the aqueous phase. For 40 of the samples sodium sulphite was added at low concentrations and the rate of oxidation of S(IV) to S(VI) established. The first order rate constant ks(IV) was found to vary over three orders of magnitude, from 10−5 to 10−2 s−1. pH and iron concentrations were found to be the most important factors affecting the rate. There was poor correlation between the rate of oxidation and the manganese, copper and zinc concentrations. The absolute values of the rate constants are lower than those used in recent modelling studies of atmospheric droplets and the importance of iron relative to manganese also differs from earlier studies.  相似文献   

20.
Nitrogen dioxide is the light absorber in the hydrocarbon system leading to production of photochemical air pollution. Studies of the reactions involved are based on the kinetics of nitrogen dioxide photolysis and the values of the rate constants derived therefrom. The photolysis of nitrogen dioxide was investigated in the 2-20 ppm concentration range. The value of the bimolecular rate constant of the reaction between oxygen atoms and nitrogen dioxide was calculated to be 5.26 × 1091 mole–1 sec–1, and thetermolecular rate constant of the reaction between oxygen atoms and nitrogen dioxide in presence of a third body is 4.24 × 10–10 12mole–2 sec–1. The rate constant for the reaction between oxygen atoms and nitric oxide in the presence of a third body was calculated to be 2.31 × 1010 12mole–2 sec–1. Nitrogen was used as the third body. In terms of order of magnitude these calculated rate constants are similar to previously reported values. However, in certain cases their use leads to an oxygen atom concentration which is 100% greater than previously calculated.  相似文献   

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